[lttng-tools.git] / src / common / runas.c

/*
 * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
 *                      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; only version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#define _GNU_SOURCE
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sched.h>
#include <sys/signal.h>

#include <common/error.h>
#include <common/compat/mman.h>
#include <common/compat/clone.h>

#include "runas.h"

#define RUNAS_CHILD_STACK_SIZE	10485760

#ifndef MAP_STACK
#define MAP_STACK		0
#endif

struct run_as_data {
	int (*cmd)(void *data);
	void *data;
	uid_t uid;
	gid_t gid;
	int retval_pipe;
};

struct run_as_mkdir_data {
	const char *path;
	mode_t mode;
};

struct run_as_open_data {
	const char *path;
	int flags;
	mode_t mode;
};

/*
 * Create recursively directory using the FULL path.
 */
static
int _mkdir_recursive(void *_data)
{
	struct run_as_mkdir_data *data = _data;
	const char *path;
	char *p, tmp[PATH_MAX];
	struct stat statbuf;
	mode_t mode;
	size_t len;
	int ret;

	path = data->path;
	mode = data->mode;

	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	if (ret < 0) {
		PERROR("snprintf mkdir");
		goto error;
	}

	len = ret;
	if (tmp[len - 1] == '/') {
		tmp[len - 1] = 0;
	}

	for (p = tmp + 1; *p; p++) {
		if (*p == '/') {
			*p = 0;
			ret = stat(tmp, &statbuf);
			if (ret < 0) {
				ret = mkdir(tmp, mode);
				if (ret < 0) {
					if (!(errno == EEXIST)) {
						PERROR("mkdir recursive");
						ret = -errno;
						goto error;
					}
				}
			}
			*p = '/';
		}
	}

	ret = mkdir(tmp, mode);
	if (ret < 0) {
		if (!(errno == EEXIST)) {
			PERROR("mkdir recursive last piece");
			ret = -errno;
		} else {
			ret = 0;
		}
	}

error:
	return ret;
}

static
int _mkdir(void *_data)
{
	struct run_as_mkdir_data *data = _data;
	return mkdir(data->path, data->mode);
}

static
int _open(void *_data)
{
	struct run_as_open_data *data = _data;
	return open(data->path, data->flags, data->mode);
}

static
int child_run_as(void *_data)
{
	struct run_as_data *data = _data;
	size_t writelen, writeleft, index;
	union {
		int i;
		char c[sizeof(int)];
	} sendret;
	int ret;

	/*
	 * Child: it is safe to drop egid and euid while sharing the
	 * file descriptors with the parent process, since we do not
	 * drop "uid": therefore, the user we are dropping egid/euid to
	 * cannot attach to this process with, e.g. ptrace, nor map this
	 * process memory.
	 */
	if (data->gid != getegid()) {
		ret = setegid(data->gid);
		if (ret < 0) {
			perror("setegid");
			return EXIT_FAILURE;
		}
	}
	if (data->uid != geteuid()) {
		ret = seteuid(data->uid);
		if (ret < 0) {
			perror("seteuid");
			return EXIT_FAILURE;
		}
	}
	/*
	 * Also set umask to 0 for mkdir executable bit.
	 */
	umask(0);
	sendret.i = (*data->cmd)(data->data);
	/* send back return value */
	writeleft = sizeof(sendret);
	index = 0;
	do {
		writelen = write(data->retval_pipe, &sendret.c[index],
				writeleft);
		if (writelen < 0) {
			perror("write");
			return EXIT_FAILURE;
		}
		writeleft -= writelen;
		index += writelen;
	} while (writeleft > 0);
	return EXIT_SUCCESS;
}

static
int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
{
	struct run_as_data run_as_data;
	int ret = 0;
	int status;
	pid_t pid;
	int retval_pipe[2];
	ssize_t readlen, readleft, index;
	void *child_stack;
	union {
		int i;
		char c[sizeof(int)];
	} retval;

	/*
	 * If we are non-root, we can only deal with our own uid.
	 */
	if (geteuid() != 0) {
		if (uid != geteuid()) {
			ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
				uid, geteuid());
			return -EPERM;
		}
	}

	ret = pipe(retval_pipe);
	if (ret < 0) {
		perror("pipe");
		retval.i = ret;
		goto end;
	}
	run_as_data.data = data;
	run_as_data.cmd = cmd;
	run_as_data.uid = uid;
	run_as_data.gid = gid;
	run_as_data.retval_pipe = retval_pipe[1];	/* write end */
	child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
		PROT_WRITE | PROT_READ,
		MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
		-1, 0);
	if (child_stack == MAP_FAILED) {
		perror("mmap");
		retval.i = -ENOMEM;
		goto close_pipe;
	}
	/*
	 * Pointing to the middle of the stack to support architectures
	 * where the stack grows up (HPPA).
	 */
	pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
		&run_as_data);
	if (pid < 0) {
		perror("clone");
		retval.i = pid;
		goto unmap_stack;
	}
	/* receive return value */
	readleft = sizeof(retval);
	index = 0;
	do {
		readlen = read(retval_pipe[0], &retval.c[index], readleft);
		if (readlen < 0) {
			perror("read");
			ret = -1;
			break;
		}
		readleft -= readlen;
		index += readlen;
	} while (readleft > 0);

	/*
	 * Parent: wait for child to return, in which case the
	 * shared memory map will have been created.
	 */
	pid = waitpid(pid, &status, 0);
	if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
		perror("wait");
		retval.i = -1;
	}
unmap_stack:
	ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
	if (ret < 0) {
		perror("munmap");
		retval.i = ret;
	}
close_pipe:
	close(retval_pipe[0]);
	close(retval_pipe[1]);
end:
	return retval.i;
}

int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
{
	struct run_as_mkdir_data data;

	DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
			path, mode, uid, gid);
	data.path = path;
	data.mode = mode;
	return run_as(_mkdir_recursive, &data, uid, gid);
}

int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
{
	struct run_as_mkdir_data data;

	DBG3("mkdir() %s with mode %d for uid %d and gid %d",
			path, mode, uid, gid);
	data.path = path;
	data.mode = mode;
	return run_as(_mkdir, &data, uid, gid);
}

/*
 * Note: open_run_as is currently not working. We'd need to pass the fd
 * opened in the child to the parent.
 */
int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
{
	struct run_as_open_data data;

	DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
			path, flags, mode, uid, gid);
	data.path = path;
	data.flags = flags;
	data.mode = mode;
	return run_as(_open, &data, uid, gid);
}
Commit	Line	Data
	1	/*
	2	* Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca>
	3	* Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	4	*
	5	* This program is free software; you can redistribute it and/or modify it
	6	* under the terms of the GNU General Public License as published by the Free
	7	* Software Foundation; only version 2 of the License.
	8	*
	9	* This program is distributed in the hope that it will be useful, but WITHOUT
	10	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	11	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	12	* more details.
	13	*
	14	* You should have received a copy of the GNU General Public License along with
	15	* this program; if not, write to the Free Software Foundation, Inc., 59 Temple
	16	* Place - Suite 330, Boston, MA 02111-1307, USA.
	17	*/
	18
	19	#define _GNU_SOURCE
	20	#include <errno.h>
	21	#include <limits.h>
	22	#include <stdio.h>
	23	#include <stdlib.h>
	24	#include <string.h>
	25	#include <sys/wait.h>
	26	#include <sys/types.h>
	27	#include <sys/stat.h>
	28	#include <unistd.h>
	29	#include <fcntl.h>
	30	#include <sched.h>
	31	#include <sys/signal.h>
	32
	33	#include <common/error.h>
	34	#include <common/compat/mman.h>
	35	#include <common/compat/clone.h>
	36
	37	#include "runas.h"
	38
	39	#define RUNAS_CHILD_STACK_SIZE 10485760
	40
	41	#ifndef MAP_STACK
	42	#define MAP_STACK 0
	43	#endif
	44
	45	struct run_as_data {
	46	int (cmd)(void data);
	47	void *data;
	48	uid_t uid;
	49	gid_t gid;
	50	int retval_pipe;
	51	};
	52
	53	struct run_as_mkdir_data {
	54	const char *path;
	55	mode_t mode;
	56	};
	57
	58	struct run_as_open_data {
	59	const char *path;
	60	int flags;
	61	mode_t mode;
	62	};
	63
	64	/*
	65	* Create recursively directory using the FULL path.
	66	*/
	67	static
	68	int _mkdir_recursive(void *_data)
	69	{
	70	struct run_as_mkdir_data *data = _data;
	71	const char *path;
	72	char *p, tmp[PATH_MAX];
	73	struct stat statbuf;
	74	mode_t mode;
	75	size_t len;
	76	int ret;
	77
	78	path = data->path;
	79	mode = data->mode;
	80
	81	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	82	if (ret < 0) {
	83	PERROR("snprintf mkdir");
	84	goto error;
	85	}
	86
	87	len = ret;
	88	if (tmp[len - 1] == '/') {
	89	tmp[len - 1] = 0;
	90	}
	91
	92	for (p = tmp + 1; *p; p++) {
	93	if (*p == '/') {
	94	*p = 0;
	95	ret = stat(tmp, &statbuf);
	96	if (ret < 0) {
	97	ret = mkdir(tmp, mode);
	98	if (ret < 0) {
	99	if (!(errno == EEXIST)) {
	100	PERROR("mkdir recursive");
	101	ret = -errno;
	102	goto error;
	103	}
	104	}
	105	}
	106	*p = '/';
	107	}
	108	}
	109
	110	ret = mkdir(tmp, mode);
	111	if (ret < 0) {
	112	if (!(errno == EEXIST)) {
	113	PERROR("mkdir recursive last piece");
	114	ret = -errno;
	115	} else {
	116	ret = 0;
	117	}
	118	}
	119
	120	error:
	121	return ret;
	122	}
	123
	124	static
	125	int _mkdir(void *_data)
	126	{
	127	struct run_as_mkdir_data *data = _data;
	128	return mkdir(data->path, data->mode);
	129	}
	130
	131	static
	132	int _open(void *_data)
	133	{
	134	struct run_as_open_data *data = _data;
	135	return open(data->path, data->flags, data->mode);
	136	}
	137
	138	static
	139	int child_run_as(void *_data)
	140	{
	141	struct run_as_data *data = _data;
	142	size_t writelen, writeleft, index;
	143	union {
	144	int i;
	145	char c[sizeof(int)];
	146	} sendret;
	147	int ret;
	148
	149	/*
	150	* Child: it is safe to drop egid and euid while sharing the
	151	* file descriptors with the parent process, since we do not
	152	* drop "uid": therefore, the user we are dropping egid/euid to
	153	* cannot attach to this process with, e.g. ptrace, nor map this
	154	* process memory.
	155	*/
	156	if (data->gid != getegid()) {
	157	ret = setegid(data->gid);
	158	if (ret < 0) {
	159	perror("setegid");
	160	return EXIT_FAILURE;
	161	}
	162	}
	163	if (data->uid != geteuid()) {
	164	ret = seteuid(data->uid);
	165	if (ret < 0) {
	166	perror("seteuid");
	167	return EXIT_FAILURE;
	168	}
	169	}
	170	/*
	171	* Also set umask to 0 for mkdir executable bit.
	172	*/
	173	umask(0);
	174	sendret.i = (*data->cmd)(data->data);
	175	/* send back return value */
	176	writeleft = sizeof(sendret);
	177	index = 0;
	178	do {
	179	writelen = write(data->retval_pipe, &sendret.c[index],
	180	writeleft);
	181	if (writelen < 0) {
	182	perror("write");
	183	return EXIT_FAILURE;
	184	}
	185	writeleft -= writelen;
	186	index += writelen;
	187	} while (writeleft > 0);
	188	return EXIT_SUCCESS;
	189	}
	190
	191	static
	192	int run_as(int (cmd)(void data), void *data, uid_t uid, gid_t gid)
	193	{
	194	struct run_as_data run_as_data;
	195	int ret = 0;
	196	int status;
	197	pid_t pid;
	198	int retval_pipe[2];
	199	ssize_t readlen, readleft, index;
	200	void *child_stack;
	201	union {
	202	int i;
	203	char c[sizeof(int)];
	204	} retval;
	205
	206	/*
	207	* If we are non-root, we can only deal with our own uid.
	208	*/
	209	if (geteuid() != 0) {
	210	if (uid != geteuid()) {
	211	ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
	212	uid, geteuid());
	213	return -EPERM;
	214	}
	215	}
	216
	217	ret = pipe(retval_pipe);
	218	if (ret < 0) {
	219	perror("pipe");
	220	retval.i = ret;
	221	goto end;
	222	}
	223	run_as_data.data = data;
	224	run_as_data.cmd = cmd;
	225	run_as_data.uid = uid;
	226	run_as_data.gid = gid;
	227	run_as_data.retval_pipe = retval_pipe[1]; /* write end */
	228	child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
	229	PROT_WRITE \| PROT_READ,
	230	MAP_PRIVATE \| MAP_GROWSDOWN \| MAP_ANONYMOUS \| MAP_STACK,
	231	-1, 0);
	232	if (child_stack == MAP_FAILED) {
	233	perror("mmap");
	234	retval.i = -ENOMEM;
	235	goto close_pipe;
	236	}
	237	/*
	238	* Pointing to the middle of the stack to support architectures
	239	* where the stack grows up (HPPA).
	240	*/
	241	pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
	242	&run_as_data);
	243	if (pid < 0) {
	244	perror("clone");
	245	retval.i = pid;
	246	goto unmap_stack;
	247	}
	248	/* receive return value */
	249	readleft = sizeof(retval);
	250	index = 0;
	251	do {
	252	readlen = read(retval_pipe[0], &retval.c[index], readleft);
	253	if (readlen < 0) {
	254	perror("read");
	255	ret = -1;
	256	break;
	257	}
	258	readleft -= readlen;
	259	index += readlen;
	260	} while (readleft > 0);
	261
	262	/*
	263	* Parent: wait for child to return, in which case the
	264	* shared memory map will have been created.
	265	*/
	266	pid = waitpid(pid, &status, 0);
	267	if (pid < 0 \|\| !WIFEXITED(status) \|\| WEXITSTATUS(status) != 0) {
	268	perror("wait");
	269	retval.i = -1;
	270	}
	271	unmap_stack:
	272	ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
	273	if (ret < 0) {
	274	perror("munmap");
	275	retval.i = ret;
	276	}
	277	close_pipe:
	278	close(retval_pipe[0]);
	279	close(retval_pipe[1]);
	280	end:
	281	return retval.i;
	282	}
	283
	284	int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
	285	{
	286	struct run_as_mkdir_data data;
	287
	288	DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
	289	path, mode, uid, gid);
	290	data.path = path;
	291	data.mode = mode;
	292	return run_as(_mkdir_recursive, &data, uid, gid);
	293	}
	294
	295	int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
	296	{
	297	struct run_as_mkdir_data data;
	298
	299	DBG3("mkdir() %s with mode %d for uid %d and gid %d",
	300	path, mode, uid, gid);
	301	data.path = path;
	302	data.mode = mode;
	303	return run_as(_mkdir, &data, uid, gid);
	304	}
	305
	306	/*
	307	* Note: open_run_as is currently not working. We'd need to pass the fd
	308	* opened in the child to the parent.
	309	*/
	310	int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
	311	{
	312	struct run_as_open_data data;
	313
	314	DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
	315	path, flags, mode, uid, gid);
	316	data.path = path;
	317	data.flags = flags;
	318	data.mode = mode;
	319	return run_as(_open, &data, uid, gid);
	320	}